This invention relates to the producing of multiple intensity or gray scale light output in a gaseous discharge display panel.
Multiple cell gas discharge display and/or memory panels of one particular type with which the present invention is concerned are characterized by an ionizable gaseous medium, at an appropriate gas pressure, in a thin gas chamber or space between a pair of opposed dielectric charge storage members. The dielectric charge storage members are typically backed by arrays of electrodes or conductors which are appropriately oriented so as to define a plurality of discrete gas discharge unit or cell sites.
In some prior art panels, the discharge cells are additionally defined by surrounding or confining physical structure such as apertures in perforated glass plates and the like so as to be physically isolated relative to other cells.
In either case, with or without the confining physical structure, electronic charges (electrons and ions) produced upon ionization of the gas volume at a selected discharge cell, when proper alternating operating potentials are applied to selected electrodes or conductors thereof, are collected upon and/or within the dielectric at specific locations defined by the cross-overs of opposite electrodes. These charges constitute an electrical field opposing the electrical field which created them so as to terminate the gas discharge for the remainder of the half cycle and aid in the initiation of a gas discharge on a succeeding opposite half cycle of applied voltage. Such dielectric charges as are stored constitute an electrical memory.
Thus, the dielectric layers prevent the passage of substantial conductive current from the conductor members to the gaseous medium and also serve as collecting surfaces for ionized gaseous medium charges (electrons and ions) during the alternate half cycles of the A.C. operating potentials. Such charges collect first at one elemental or discrete dielectric surface area and then at an opposing elemental or discrete dielectric surface area on alternate half cycles to constitute the electrical memory.
An example of a panel structure containing non-physically isolated or open discharge cells is disclosed in U.S. Pat. No. 3,499,167 (incorporated herein by reference) issued to Theodore C. Baker, et al.
An example of a panel containing physically isolated cells is disclosed in the article by D. L. Bitzer and H. G. Slottow entitled "The Plasma Display Panel-A Digitally Addressable Display With Inherent Memory". Proceeding of the Fall Joint Computer Conference, IEEE, San Francisco, Calif., November, 1966, pages 541-547 and also in U.S. Pat. No. 3,559,190 (incorporated herein by reference) issued to D. L. Bitzer et al.
A monolithic or single substrate device structure may also be used as disclosed in U.S. Pat. Nos. 3,860,846 (Mayer) and 3,896,327 (Schermerhorn), both incorporated herein by reference.
In the construction of the panel, a continuous volume of ionizable gas is confined between a pair of dielectric surfaces backed by electrode arrays typically forming matrix elements. The two electrode arrays may be orthogonally related sets of parallel lines (but any other configuration of electrode arrays may be used). The two arrays of electrodes define at their crossovers a plurality of opposed pairs of charge storage areas on the opposing surfaces of the dielectric members bonding or confining the gas. Thus, for a first array of R parallel row electrodes and a second array of C parallel column electrodes, the number of gas discharge cells will be the multiple of R times C and the number of dielectric charge storage locations will be twice the number of discharge cells.
The state of the art explanation as to the charge storage mechanism of the A.C. gas discharge memory panel appears in the U.S. Pat. No. 3,559,190 (Bitzer, et al.) and U.S. Pat. No. 3,499,167 (Baker, et al.), both of which patents are incorporated by reference into the present disclosure. The prior art typically explains the memory mechanism in terms of the storage or accumulation of wall charges on a dielectric surface. However, this is a theoretical physics mechanism, and it is not known for certain whether the wall charges (constituting the so-called memory) are stored on the surface of the dielectric member or beneath the dielectric. Perhaps, it is some combination of the two mechanisms with the wall charges being stored both on and beneath the dielectric surface. In any case, the present invention is not dependent upon any particular theoretical explanation as to how the charges are retained and stored by the dielectric. The important fact is that wall charges are in some way retained and stored by a dielectric member in an A.C. gas discharge device; i.e., of the types and structures disclosed by the U.S. patents issued to Bitzer, et al., Baker, et al., Mayer, and Schermerhorn incorporated by reference into the present disclosure.
The use of an A.C. gas discharge memory panel as a television device depends upon so-called gray scale or multiple intensity operation. A number of techniques have been disclosed in the prior art for gray scale operation of a gas discharge device. For example, these include spatial gray scale as disclosed in U.S. Pat. No. 3,845,243 issued to Schmersal et al.; time modulation of bistable states as disclosed in U.S. Pat. No. 3,863,023 also issued to Schmersal et al.; ordered dither; and geometric arrangements such as stacked panels. These prior art gray scale methods generally depend upon the operation of the A.C. gas discharge device in the bistable memory mode. As will be discussed in detail hereinafter, the present invention is directed to the gray scale operation of an A.C. plasma panel in a non-memory or non-bistable mode as disclosed in Nolan U.S. Pat. No. 4,002,828 incorporated by reference into the present disclosure.